Technical Field
Embodiments of the invention relate generally to pulverizer mills, also referred to hereinafter simply as “mills,” and more specifically, to a system and method for adjusting a depth of a material bed in a pulverizer mill.
Discussion of Art
Pulverizer mills are devices that size reduce a material up into particles. For example, many pulverizer mills grind solid fuels, e.g., coal, prior to combustion of the fuels in a furnace of a power plant. Many such mills grind solid fuels via grinding rollers that crush the fuels against a hard rotating surface known as a “bowl.” The grinding rollers are attached to journal assemblies via bearings which allow the rollers to rotate. When a solid fuel is placed into the bowl, the rotation of the bowl causes the solid fuel to move under the grinding rollers, which in turn causes the grinding rollers to rotate in place. The journal assemblies also apply a downward force to the grinding rollers. Due to the downward force applied by the journal assemblies, the solid fuel is crushed/pulverized by the rollers.
The pulverized fuel then flows through a classifier which allows fine particles, i.e., particles that are at or below a maximum particle size, to flow out of the pulverizer mill, and restricts coarse particles, i.e., particles that are above the maximum particle size, from leaving the mill. The maximum size of particles allowed to flow/pass through a classifier is known as the “fineness” of the classifier, wherein a “high fineness” has a maximum particle size that is smaller than a “low fineness.” In other words, the fineness of a classifier is a controlled distribution of the particles sizes allowed to flow out of the pulverizer mill.
In many mills, the solid fuel is first fed from a feeder via gravity onto a central region of the bowl known as the “table,” and then allowed to centrifugally flow towards the outer circumference of the bowl as the bowl rotates. Many such pulverizer mills include a ring, known as an “extension ring,” “dam ring,” and/or “bowl ring,” disposed along the outer edge of the bowl which has a first order influence on the depth of the bed formed by the solid fuel within the bowl, e.g., the greater or shorter the amount the ring extends away from the bowl, the deeper or shallower the depth of the fuel bed, respectively. Such extension rings, however, are presently fixed in place with respect to the bowl such that the amount the ring extends away from the bowl cannot be changed without shutting down the encompassing pulverizer mill, i.e., stopping rotation of the bowl, and exchanging out one extension ring for another. Thus, the depth of the material bed in present pulverizer mill designs is fixed, i.e., not adjustable, while the pulverizer mill is operating, i.e., while the bowl is rotating.
What is needed, therefore, is an improved system and method for adjusting the depth of a material bed in a pulverizer mill.